For toothpaste manufacturers, the stringiness of the toothpaste ribbon has historically been and is today an important parameter of concern. High volume manufacturers typically package toothpaste in laminated tubes using high speed filling lines that are capable of filling 80 to 200 tubes per minute. To meet the demands of such production, it is important that the toothpaste ribbon cuts off sharply from the tube. If toothpaste remains in the sealing portion of the lamitube, tube sealing could be faulty resulting in the opening of the tube. Also, toothpaste string coming out of the tube could cause blackening on the outside portion of the tube in the sealing area due to burning while it is being sealed. Open and blackened tubes are rejected during production. On the consumer side, stringy toothpaste gives a shabby look to the toothpaste nozzle during usage. These problems are inherent with a toothpaste that tails or is stringy. To avoid or minimize these problems, a toothpaste formulation is desired that provides a sharp cut off, i.e., a toothpaste that is not stringy or does not tail.
Toothpaste generally contains a polishing agent or abrasive, humectant, thickener or binder, water, foaming agent and flavoring agents. The humectant and water are also referred to collectively as the vehicle. In addition, agents that provide therapeutic or cosmetic benefits may be incorporated such as fluoride and tartar control agents. In seeking to provide a non-stringy toothpaste, the formulation must maintain other excellent physical properties to which the consumer is accustomed. For consumer satisfaction these properties should provide a toothpaste that has appealing taste, good cleansing effect, is easy to rinse, excellent mouth feel, and chemical and physical stability. Furthermore, these properties should be provided in a toothpaste that is cost effective for the consumer.
The formulation properties of a toothpaste will depend on the inherent properties of the binder, abrasive, humectant, water and other components of the formulation, and they will also depend on how these components behave in complex mixtures with each other. In general, stringiness will be a function of the type and amount of binder and abrasive used in the toothpaste formulation. To a lesser extent, stringiness will also be effected by the choice of humectant. Among the commonly used binders, for example, carboxymethylcellulose (CMC) is known to generally promote stringiness while carrageenan reduces stringiness. Among the commonly used abrasives, silica generally enhances stringiness relative to chalk and dicalcium phosphate (DCP).
The generic term carrageenan is applied to dozens of similar polysaccharides derived from seaweed. All carrageenans contain repeating galactose units joined by alternating .beta.1.fwdarw.3 and .alpha.1.fwdarw.4 glycosidic linkages and are partially sulfated. The types of carrageenans may be distinguished, in part, by their degree of sulfation. Kappa carrageenan has a repeating unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose providing a sulfate ester content of about 18 to 25%. Iota carrageenan has a repeating unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose-2-sulfate providing a sulfate ester content of about 25 to 34%. Lambda carrageenan has a repeating unit of D-galactose-2-sulfate-D-galactose-2,6-disulfate providing a sulfate ester content of about 30 to 40%.
The carrageenans forms gels that are thixotropic. Such gels are reported to exhibit excellent extrudability, flavor release and rinsability. The use of kappa and iota carrageenan as binders in gel toothpaste is known to also provide a toothpaste that is non-stringy. However, as U.S. Pat. No. 4,604,280 notes a problem associated with compositions made using carrageenan is that the thickness or viscosity of the composition tends to decrease when the composition is subjected to mechanical working at a temperature below the gel-sol temperature. For carrageenan, the gel-sol temperature is in the range of about 450 to 49.degree. C. Sometimes a minor working below this temperature can cause a substantial decrease in viscosity. To compensate for such loss of viscosity, it is often necessary to employ additional amounts of carrageenan to the formulation than would otherwise be necessary. Carrageenan is therefore often employed at a weight concentration in excess of one percent.
Of the types of carrageenan, iota, kappa and lambda, that have been used in toothpaste formulations, iota carrageenan is usually preferred. This preference is due in part to a difference in hardening effect. Relative to gels based on iota carrageenan, gels based on kappa carrageenan are reported to harden more readily on the shelf. Toothpastes that harden in such a manner become difficult to squeeze from the tube. Also, relative to the iota form, gels based on kappa carrageenan are more likely to have a syneresis problem; i.e., they will be more likely to have water separate from the gel. Toothpaste products are deemed unacceptable if they are not stable against such phase separation. For these reasons, when carrageenan is employed as a binder in gel toothpaste it is usually the iota form that is chosen.
It is an objective of this invention to provide a non-stringy gel toothpaste which is comprised of kappa carrageenan as a major component of the binder but without the aforementioned stability problems associated with kappa carrageenan. It is a further objective to provide such a toothpaste where the concentration of kappa carrageenan is relatively low.